1. Field of the Invention
The present invention generally relates to heat treatment apparatuses and more particularly to a heat treatment apparatus which performs an anneal process or a chemical vapor deposition (CVD) process by heating an object to be processed, such as a single crystalline substrate or a glass substrate, with a lamp and a quartz window used for such a heat treatment apparatus. The present invention is suitable for a rapid thermal processing (RTP: Rapid Thermal Processing) used for manufacturing semiconductor devices, such as a memory or an integrated circuit (IC). The rapid thermal processing (RTP) includes rapid thermal annealing (RTA), rapid thermal cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD), rapid thermal oxidization (RTO) and rapid thermal nitriding (RTN).
2. Description of the Related Art
Generally, in order to manufacture a semiconductor integrated circuit, various kinds of heat treatment, such as a film deposition process, an anneal process, an oxidization diffusion process, a sputtering process, an etching process and a nitriding processing may be repeatedly performed on a silicon substrate such as a semiconductor wafer a plurality of times.
Since yield rate and quality of semiconductor manufacturing processes can be improved, the RTP technology to rise and drop the temperature of the wafer (object to he processed) has attracted attention. A conventional RTP apparatus generally comprises: a single-wafer chamber (process chamber) for accommodating an object to be processed (for example, a semiconductor wafer, a glass substrate for photograph masks, a glass substrate for a liquid-crystal display or a substrate for optical discs); a reflector (reflective board) arranged at the opposite side of the object to be processed with respect to a quartz window arranged in the interior of the process chamber; and a heating lamp (for example, halogen lamp) arranged at an upper part or above the quartz window, and the lamp.
The reflector is made of aluminum, and gold plating is given to a reflective part thereof. A cooling mechanism such as a cooling pipe is provided so as to prevent temperature breakage of the reflector (for example, exfoliation of gold plating due to a high temperature). The cooling mechanism is provided so as to prevent the reflector from being an obstacle of cooling the object to be processed at the time of cooling. The rapid temperature rising demanded for the RTP technology is dependent on the directivity of the optical irradiation to the object to be processed and the power density of the lamp.
The quartz window may be in the shape of a board, or can be in the form of tube which can accommodate the object to be processed. When maintaining a negative pressure environment in the process chamber by evacuating gasses in the process chamber by a vacuum pump, a thickness of the quartz window is set to, for example, about 30 to 40 mm so as to maintain the pressure difference between the internal pressure and the atmospheric pressure. The quartz window may be formed in a curved shape having a reduced thickness so as to prevent generation of a thermal stress due to temperature difference generated by a temperature rise.
A plurality of halogen lamps are arranged so as to uniformly heat the object to be processed. The reflector reflects the infrared rays irradiated from the halogen lamps toward the object to be processed. The process chamber is typically provided with a gate valve on a sidewall thereof so as to carry in and out the object to be processed. Moreover, a gas supply nozzle, which introduces a process gas used for heat treatment, is connected to the sidewall of the process chamber.
The temperature of the object to be processed affects the quality of process such as, for example, a thickness of a film in a film deposition process, etc. For this reason, it is necessary to know the correct temperature of the object to be processed. In order to attain high-speed heating and high-speed cooling, a temperature measuring device which measures the temperature of the object to be processed is provided in the process chamber. The temperature measuring device may be constituted by a thermocouple. However, since it is necessary to bring the thermocouple into contact with the object to be processed, there is a possibility that the processed body is polluted with the metal which constitutes the thermocouple. Therefore, there is proposed a payro meter as a temperature measuring device which detects an infrared intensity emitted and computes a temperature of an object to be processed from the back side thereof based on the detected infrared intensity. The payro meter computes the temperature of the object to be processed by carrying out a temperature conversion by an emissivity of the object to be processed according to the following expression:Em(T)=εEBB(T)  (1)where, EBB(T) expresses a radiation intensity from a black body having the temperature T; Em(T) expresses a radiation intensity measured from the object to be processed having the temperature T; ε expresses a rate of radiation of the object to be processed.
In operation, the object to be processed is introduced into the process chamber through the gate valve. The peripheral portion of the object to be processed is supported by a holder. At the time of heat treatment, process gases such as nitrogen gas and oxygen gas, are introduced into the process chamber through the gas supply nozzle. On the other hand, the infrared ray irradiated from the halogen lamps is absorbed by the object to be processed, thereby, rising the temperature of the object to be processed.
Recently, a demand for a rapid temperature rise of RTP has been increased so as to achieve a high-quality process of an object to be processed and improve a throughput. For example, there is a demand for increasing a temperature rising rate from 90 degrees/sec to 250 degrees/sec.
A support ring on which an object to be processed such as a silicone substrate is placed is formed of ceramics (for example, SiC) having excellent heat resistance. There is a difference in heat capacity between the support ring and the silicon substrate, which results in a difference in temperature rise. For this reason, the temperature rising rate of a periphery of the object to be processed, which periphery contact with the support ring, is smaller than that of the center of the object to be processed. Thus, there is a problem in that it is difficult to carry out a rapid and uniform temperature rise over the entire surface of the object to be processed. As measures for solving such a problem, the present inventors made a study on heating the periphery of the object to be processed by a larger power than that applied to the center of the object. Additionally, the reflector also deteriorates due to heating with a large power. However, a high-output lamp has a service life shorter than a low-output lamp. Similarly, the reflector for high-output lamps also has a service life shorter than the reflector for low-output lamps. Consequently, in order to exchange the life-expired lamps and reflectors located in the periphery of a lamp house, the whole lamp house including the lamps and reflectors located in the center of the lamp house, which are still usable, must be exchanged simultaneously, which results in uneconomical operation.
A rapid temperature rise depends on a power density of a lamp and a directivity of the optical irradiation from the lamp to an object to be processed. In the case of a single end lamp 2, which has only one electrode part 3 like the conventional lamp, an illuminant (coil 4 in the figure) of the lamp 2 is perpendicularly formed to the object to be processed, as shown in FIG. 1. Here, FIG. 1 is an illustrative cross-sectional view showing the shape of the conventional lamp. Since the coil 4 projects a light in a direction perpendicular to the axial center of the coil 4 concerned, it is impossible for the lamp 2 alone to control the directivity. Conventionally, The directivity of the lamp 2 is obtained by providing a cylindrical reflector 5 or reflective film around the lamp 2 so as to cover the lamp 2. However, the reflector 5 and the reflective film cannot reflect light 100%. Therefore, the light is absorbed or diffused to some extent, and there is a problem in that the energy of the lamp light decreases. Since the reflection takes place a plurality of times at the reflector 5 and the reflective surface, the power density of the light irradiated onto the object to be processed may become less than one half of the light at the time of projection. On the other hand, it can be considered to increase the density of power reaching the object to be processed by increasing the electric power supplied to the lamp 2. However, such an approach causes an increase in the power consumption, which is not economically preferable. Therefore, conventionally, even if the energy of the lamp light decreases, the reflector 5 or the reflective film had to be used so as to obtain a desired directivity of the lamp 2.